Rework hypervisor detection

[Conrad Meyer]

Hi John,

I don't have access to phabricator so I'll try and review in email.

> +#ifdef XEN
> +int vm_guest = VM_GUEST_XEN;
> +#else
> +int vm_guest = VM_GUEST_NO; /* Running as virtual machine guest? */
> +#endif

The whitespace between 'int' and 'vm_guest' in the second line seems
wrong (extra space?).

For vmware_hvcall() in x86/include/vmware.h, are you sure the inline
assembly is correct? Have you tried the detection on a VMware VM?
VMware's documentation specifies the arguments in a different
order[0], and at Isilon when we tried the port-based detection in a
slightly older revision of CURRENT, it didn't work (IIRC).

Everything else looks good to me, thanks.

[0]: http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1009458

Best,
Conrad